1. Field of the Invention
The present invention relates to a power supply system provided with a photovoltaic generator.
2. Description of the Related Art
Conventional systems are known in which a photovoltaic generator and a load are connected to each other through a DC/AC inverter (for example, see Japanese Patent Application Laid-open No. 6-133462).
To conduct the generation of electric power by a photovoltaic generator with the best efficiency, it is required that the operational point of the photovoltaic generator is brought into an optimal operational point.
However, the optimal operational point varies with the variation in insolation amount, and on the other hand, the current-voltage characteristic of the load is substantially constant and the operational point of the photovoltaic generator is determined by the current-voltage characteristic of the load. For this reason, it is difficult in the conventionally known system to keep the operational point of the photovoltaic generator always at the optimal operational point.
Accordingly, it is an object of the present invention to provide a power supply system of the above-described type, wherein the operational point of the photovoltaic generator is kept at the optimal operational point, and a required electric power can be supplied stably to the load.
To achieve the above object, according to the present invention, there is provided a power supply system comprising a photovoltaic generator, a load to which electric power is supplied from the photovoltaic generator, an electrical system capable of receiving a portion of the electric power generated by the photovoltaic generator and supplying the electric power to the load, and a control unit for controlling the reception and supply of the electric power by the electrical system. In order to ensure that the photovoltaic generator generates electric power at an optimal operational point, the control unit adapted in such a manner so as to not operate when the maximum electric power Pmax generated by the photovoltaic generator and an electric power PL consumed by the load are equal to each other (Pmax=PL), and to operate when Pmax greater than PL, thereby permitting the electrical system to receive surplus electric power xcex94P1 (=Pmaxxe2x88x92PL), and to operate when Pmax less than PL, thereby supplying a deficient electric power xcex94P2 (=PLxe2x88x92Pmax) from the electrical system to the load.
With the above arrangement, when the maximum electric power Pmax generated by the photovoltaic generator and the electric power PL consumed by the load are equal to each other (Pmax=PL), the load is operated, and the current-voltage characteristic of the load corresponds to the optimal operational point of the photovoltaic generator and hence, the operational point of the photovoltaic generator is at the optimal operational point. In this case, the control unit need not be operated.
When Pmax greater than PL, the load is operated, but the current-voltage characteristic of the load does not correspond to the optimal operational point of the photovoltaic generator and hence, the operational point of the photovoltaic generator is not at the optimal operational point. Then, if the surplus electric power xcex94P1 is allowed to be received in the electrical system, the same state is provided as when the power consumed in the load is equal to PL+xcex94P1. Namely, the current-voltage characteristic of the load corresponds to the optimal operational point of the photovoltaic generator, because Pmax=PL+xcex94P1. Thus, the operational point for the photovoltaic generator is at the optimal operational point.
When Pmax less than PL, the load is incapable of being operated. Therefore, if the deficient electric power xcex94P2 is supplied from the electrical system to the load, the load is operated to provide the same state as when the electric power consumed in the load is equal to PLxe2x88x92xcex94P2. Namely, the current-voltage characteristic of the load corresponds to the optimal operational point of the photovoltaic generator, whereby the operational point of the photovoltaic generator is brought into the optimal operational point. Thus, it is possible to ensure that the operational point of the photovoltaic generator is kept at the optimal operational point, and to stably supply a required electric power to the load.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.